On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Lasers are the pillars of modern optics and sensing. Microlasers based on whispering-gallery modes (WGMs) are miniature in size and have excellent lasing characteristics suitable for biosensing. WGM lasers have been used for label-free detection of single virus particles, detection of molecular electrostatic changes at biointerfaces, and barcode-type live-cell tagging and tracking. The most recent advances in biosensing with WGM microlasers are described in this review. We cover the basic concepts of WGM resonators, the integration of gain media into various active WGM sensors and devices, and the cutting-edge advances in photonic devices for micro- and nanoprobing of biological samples that can be integrated with WGM lasers.

/pdf/review-of-biosensing-with-whispering-gallery-mode-lasers-87aeqiiato.pdf

Review of biosensing with whispering-gallery mode lasers

Poly(ethylene glycol) (PEG)-stabilized liposomes were recently shown to exhibit differences in cell uptake that were linked to the liposome charge. To determine the differences and similarities between charged and uncharged PEG-decorated liposomes, we directly measured the forces between two supported, neutral bilayers with terminally grafted PEG chains. The measurements were performed with the surface force apparatus. The force profiles were similar to those measured with negatively charged PEG conjugates of 1, 2-distearoyl-sn-glycero-3-phosphatidyl ethanolamine (DSPE), except that they lacked the longer ranged electrostatic repulsion observed with the charged compound. Theories for simple polymers describe the forces between end-grafted polymer chains on neutral bilayers. The force measurements were complemented by surface plasmon resonance studies of protein adsorption onto these layers. The lack of electrostatic forces reduced the adsorption of positively charged proteins and enhanced the adsorption of negatively charged ones. The absence of charge also allowed us to determine how membrane charge and the polymer grafting density independently affect protein adsorption on the coated membranes. Such studies suggest the physical basis of the different interactions of charged and uncharged liposomes with proteins and cells.

Measurements of interbilayer forces and protein adsorption on uncharged lipid bilayers displaying poly(ethylene glycol) chains.

The Visible Light Photon Counter (VLPC) features high quantum efficiency and low pulse height dispersion. These properties make it ideal for efficient photon number state detection. The ability to perform efficient photon number state detection is important in many quantum information processing applications, including recent proposals for performing quantum computation with linear optical elements. In this paper we investigate the unique capabilities of the VLPC. The efficiency of the detector and cryogenic system is measured at 543nm wavelengths to be 85%. A picosecond pulsed laser is then used to excite the detector with pulses having average photon numbers ranging from 3-5. The output of the VLPC is used to discriminate photon numbers in a pulse. The error probability for number state discrimination is an increasing function of the number of photons, due to buildup of multiplication noise. This puts an ultimate limit on the ability of the VLPC to do number state detection. For many applications, it is sufficient to discriminate between 1 and more than one detected photon. The VLPC can do this with 99% accuracy.

https://arxiv.org/pdf/quant-ph/0308054.pdf

High Efficiency Photon Number Detection for Quantum Information Processing

Microlasers, relying on the strong coupling between active particles and optical microcavity, exhibit fundamental differences from conventional lasers, such as multi-threshold/thresholdless behavior and nonclassical photon emission. As light sources, microlasers possess extensive applications in precision measurement, quantum information processing, and biochemical sensing. Here we propose a whispering-gallery-mode microlaser scheme, where ultracold alkaline-earth metal atoms, i.e., gain medium, are tightly confined in a two-color evanescent lattice that is in the ring shape and formed around a microsphere. To suppress the influence of the lattice-induced ac Stark shift on the moderately-narrow-linewidth laser transition, the red-detuned trapping beams operate at a magic wavelength while the wavelength of the blue-detuned trapping beam is set close to the other magic wavelength. The tiny mode volume and high quality factor of the microsphere ensure the strong atom-microcavity coupling in the bad-cavity regime. As a result, both saturation photon and critical atom numbers, which characterize the laser performance, are substantially reduced below unity. We explore the lasing action of the coupled system by using the Monte Carlo approach. Our scheme may be potentially generalized to the microlasers based on the forbidden clock transitions, holding the prospect for microscale active optical clocks in precision measurement and frequency metrology.

/pdf/microscale-whispering-gallery-mode-light-sources-with-3yfd9cj5k5.pdf

Microscale whispering-gallery-mode light sources with lattice-confined atoms.

Parity-time (PT) symmetric lasers exploit the modulation of optical gain and loss and have led to important fundamental demonstrations in non-Hermitian physics. The current theoretical analysis of PT-symmetric laser physics is performed on the basis of the adiabatic elimination of the medium polarization. This approximation doesn’t hold true for a more general optical system with strong photon-particle interactions, where the Rabi oscillation of active particles plays a non-negligible role in the lasing action. Here, we propose a model that takes into account the internal dynamics of active particles and numerically investigate the PT symmetry of macroscopic- and microscopic-sized laser systems that operate in the strong-coupling regime. The distinct phase diagrams are drawn according to the features of intracavity photon numbers and emission spectra. Our work extends the PT-symmetric optics from the weak- to the strong-coupling limit, potentially paving the way towards nonclassical PT-symmetric light sources for integrated photonic networks and ultrasensitive sensors. Early studies of lasing in parity-time(PT)-symmetric systems typically make use of the adiabatic elimination of the medium polarization. Here, the authors present a theoretical investigation of a realistic scenario where a laser is coupled to a passive optical cavity and study PT symmetry breaking in the strong light-matter coupling regime, finding nonclassical emission behavior in the microscopic limit.

/pdf/spontaneous-pt-symmetry-breaking-in-lasing-dynamics-4mne030zyo.pdf

Spontaneous PT-symmetry breaking in lasing dynamics

Optical Whispering Gallery Modes for Biosensing: From Physical Principles to Applications

This paper uses the Allan variance to analyze the frequency deviations that accumulate throughout the single-molecule detection in to extract information about the single-molecule processes even when the individual single-molecule events are obscured by noises.

https://link.aps.org/pdf/10.1103/PhysRevResearch.3.023087

Allan deviation tells the binding properties in single-molecule sensing with whispering-gallery-mode optical microcavities

The interaction of highly coherent light and matter is the key in the science of measurement. In the classical electromagnetic theory, the absorption and dispersion properties of the light propagation in a medium are described by the classical Lorentz oscillator model. The unavoidable phase and intensity fluctuations of a light field, which are commonly characterized by the first- and second-order correlation functions, respectively, broaden the light spectrum and restrict its practical applications in metrology. In order to suppress the spectral linewidth, the light’s frequency is usually stabilized to an optical resonator. Several light-based sensing applications, such as the gravity-wave detection and optical clocks, are briefly introduced.

Sensing with Light

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